The present invention is directed, in general, to wireless communication systems and, more specifically, to a combined system for monitoring receiver gain and measuring receiver antenna impedance match in a base station in a wireless network.
In order to increase the number of subscribers that can be serviced in a single wireless network, frequency reuse is maximized by making individual cell sites smaller and using a greater number of cell sites to cover the same geographical area. Accordingly, the greater number of base transceiver stations increases infrastructure costs. To offset this increased cost, wireless service providers continually implement any improvements that may reduce equipment costs, maintenance and repair costs, and operating costs, or that may increase service quality and reliability, and the number of subscribers that the cellular system can service.
Wireless service providers use a variety of test equipment to monitor the performance of the RF receiver and the RF transmitter of a base transceiver station (BTS). The test equipment may monitor a variety of signal parameters in the RF transmitter, including adjacent channel power ratio (ACPR), spectral purity (including in-band and out-of-band spurious components), occupied bandwidth, RHO, frequency error, and code domain power. The test equipment may also perform a variety of test functions in the RF receiver, including receive antenna impedance matching and receiver calibration. Preferably, the signal parameters are remotely monitored from a central location, so that a wireless service provider can avoid the expense of sending maintenance crews into the field to test each BTS individually. Additionally, a remote monitoring system can detect the failure of an RF transmitter or an RF receiver nearly instantaneously.
Unfortunately, adding some types of test equipment, such as spectrum analyzers, to a BTS significantly increases the cost of the BTS. In some cases, the cost of the test equipment may be greater than the cost of the BTS itself. As a result, wireless service providers frequently do not install test equipment in base transceiver stations, or install only a limited amount of test equipment to test only some of the functions of the BTS. The remaining functions must be monitored by maintenance crews using portable test equipment.
There is therefore a need in the art for inexpensive test equipment that may be implemented as part of the base station. In particular, there is a need for integrated test equipment that can perform more than one type of test in a base transceiver station. More particularly, there is a need for integrated test equipment that can be used to calibrate the gain of the receive path of the receiver and that can also be used to measure the impedance match of the receiver antenna.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a measurement and calibration circuit for use in an RF transceiver comprising an antenna and an RF receiver coupled to the antenna and having a receive path comprising circuitry capable of amplifying an incoming signal received from the antenna. In an advantageous embodiment of the present invention, the measurement and calibration circuit comprises: 1) a test signal generator capable of generating a test signal having a known amplitude and a known frequency; 2) a switch having an input coupled to the test signal generator for receiving the test signal, a first output coupled to an input of the receive path, and a second output coupled to the antenna; 3) a test controller capable of causing the switch to directly inject the test signal into the input of the receive path and capable of causing the switch to inject the test signal into the antenna, wherein the antenna at least partially reflects the test signal into the receive path; and 4) a signal monitor coupled to an output of the receive path capable of measuring the direct injected test signal and the reflected test signal.
In one embodiment of the present invention, the signal monitor is capable of adjusting a gain of the receive path.
In another embodiment of the present invention, the known frequency of the test signal is the center frequency of the RF receiver.
In still another embodiment of the present invention, the test signal generator comprises a transmitter local oscillator capable of generating a transmitter carrier signal used by an RF transmitter of the RF transceiver, a test local oscillator capable of generating a single frequency reference signal, and an RF mixer capable of mixing the transmitter carrier signal and the single frequency reference signal.
In yet another embodiment of the present invention, a frequency of the single frequency reference signal is equal to a frequency difference between a center frequency of the RF transmitter and a center frequency of the RF receiver.
In a further embodiment of the present invention, the mixing by the RF mixer of the transmitter carrier signal and the single frequency reference signal is a subtractive mixing that generates the test signal at a center frequency of the RF receiver.
In a still further embodiment of the present invention, the signal monitor compares a measured value of the direct injected test signal and a measured value of the reflected test signal to determine an impedance match of the antenna.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9cor,xe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.